INDUCTION MOTOR SPEED CONTROL SIMULATION FOR TORQUE SPEED CHARACTERISTIC

Transcription

1 Volume-3, Issue-3, March-215 INDUCTION MOTOR SPEED CONTROL SIMULATION FOR TORQUE SPEED CHARACTERISTIC 1 BHAGYASHREE SHIKKEWAL, 2 PRACHI M. PALPANKAR, 3 PRIYA DUGGAL 1 PCE Nagpur, 2 DBACER Nagpur, 3 DBACER Nagpur, prachimpalpankar@gmail.com, priyaduggal5@gmail.com, bhagyashreesgi@rediffmail.com Abstract- In case of MATLAB, the proper state equations should be obtained in order to describe the power conversion circuits. With the state equations, the circuit can be easily modeled by using the functional blocks, which are supported in MATLAB Simulink. Particular, in MATLAB, the various kinds of control algorithms can be easily implemented without using actual analog components. Using the switching function concept, the power inverter circuits can be modelled according to their functions, rather than circuit topologies, by doing this the run time is reduced. Further the generated phase voltages using the switching function concept are fed to the three-phase Induction motor, for observing the Induction motor speed-time and torque-time characteristics. Keywords- Induction Motor, Sinusoidal Pulse Width Modulation, Switching Function, Voltage Source Inverter. I. INTRODUCTION As the voltage and current ratings and switching characteristics of power semiconductor devices keep improving, the range of applications continues to expand in areas such as lamp controls, power supplies to motion control, factory automation, transportation, energy storage and electric power transmission and distribution. The technological advances made in the field of power semiconductor devices over the last two decades, have led to the development of power semiconductor devices with high power ratings and very good switching performances. Some of the popular power semiconductor devices available in the market today include Power MOS Field Effect Transistors (Power MOSFETs), Insulated Gate Bipolar Transistors (IGBTs) and Gate Turn off Thyristors (GTOs). Three-phase voltage source inverters are widely used in variable speed ac motor drives applications since they provide variable voltage and variable frequency output through pulse width modulation control. Continuous improvement in terms of cost and high switching frequency of power semiconductor devices and development of machine control algorithm leads to growing interest in more precise PWM techniques. The most widely used PWM method is the carrier-based sine-triangle PWM method due to simple implementation in both analog and digital realization. On the other hand, the main advantages of modern power electronic converters, such as high efficiency, low weight, small dimensions, fast operation, and high power densities, are being achieved through the use of the so-called switch mode operation, in which power semiconductor devices are controlled in ON=OFF fashion. The three-phase induction motors are the most widely used electric motors in industry. They run at essentially constant speed from no-load to full-load. However, the speed is frequency dependent and consequently these motors are not easily adapted to speed control. We usually prefer d.c. motors when large speed variations are required. Nevertheless, the 3-phase induction motors are simple, rugged, low-priced, easy to maintain and can be manufactured with characteristics to suit most industrial requirements. Single-phase induction motors are used extensively for smaller loads, such as household appliances like fans. Although traditionally used in fixed-speed service, induction motors are increasingly being used with variable-frequency drives (VFDs) in variable-speed service. VFDs offer especially important energy savings opportunities for existing and prospective induction motors in variable-torque centrifugal fan, pump and compressor load applications. Squirrel cage induction motors are very widely used in both fixed-speed and VFD applications. The generated phase voltages using the switching function concept are fed to the three-phase Induction motor, for observing the Induction motor speed-time and torque-time characteristics. II. GENERATION OF SWITCHING FUNCTION The switching function 1_a,b,c are generated by comparing the sinusoidal waves of, 12, -12 phase shift to carrier wave i.e. the high frequency triangular wave, the gate pulses are obtained, these are SPWM pulses, which are used for calculating the output Phase and Line voltages of three-phase Inverter. 31

2 Volume-3, Issue-3, March-215 A. Generation of Vao, Vbo, Vco, Vno (11) Fig. 1 Three phase inverter with induction motor load For calculating, the Line voltages and Phase voltages for three-phase Induction motor, we are required to calculate the voltages Vao, Vbo, Vco, Vno using the specified formulae....(12) (71)..(13) (72).(14) (73) Where, Ψmq = Xml..... (15) Ψmd = Xml..... (16)..... Vao = Vd/2 * (SF1_a).. (1) Vbo = Vd/2 * (SF1_b).. (2) Vco = Vd/2 * (SF1_c).. (3) Vno= 1/3(Vao +Vbo + Vco).. (4) B. Generation of Phase voltage Van, Vbn, Vcn Further, after calculating the voltage Vao, Vbo, Vco, Vno,using the specified formulae,we are calculating the Phase voltages Van, Vbn, Vcn. Van =Vao Vno.. (5) Vbn =Vbo Vno.. (6) Vcn=Vco Vno (7) C. Generation of line voltages Vab, Vbc, Vca For obtaining the Line voltages Vab, Vbc, Vca,we require,the previously calculated Vao, Vbo, Vco and these line voltages are calculated using the formulae mentioned below. Vab= Vao-Vbo.. (8) Vbc= Vbo-Vco.. (9) Vca= Vco-Vao.. (1) III. MODELLING OF THREE PHASE INDUCTION MOTOR Xml = 1/.. (17) Currents are calculated using the above flux linkages; Iqs =.. (18) Ids =.. (19) iqr =.. (2) idr =.. (21) Torque and Speed are determined using; Te = (22) ωr =.. (23) IV. PARAMETERS USED For Three-phase Inverter Supply voltage =3V Frequency of sin wave =5Hz Frequency of carrier wave =1 Hz Amplitude of sine wave =.8 Amplitude of carrier wave =1 Modulation index =.8.. For Three-phase Induction motor Frequency (f) =5 Hz Stator Resistance (Rs) =.435 Rotor Resistance (Rr) =.816 Leakage Reactance of Stator (Xls) =.754 Leakage Reactance of Rotor (Xlr) =.754 No.of Poles (P) =4 Moment of inertia (J) =.89 Mutual leakage Reactance (Xml) =26.13 Fig.2 The dq equivalent circuit of an Induction Motor Driving the model equation can be generated from dq equivalent circuit of induction motor shown above. The flux linkages equation associated with the circuit can be found as, V. RESULTS OF PHASE VOLTAGES C. Simulation model of Van Van =Vao Vno.. (24) Output Van 32

3 2 Volume-3, Issue-3, March-215 V a n V b n V c n Fig 3 Simulation output of Van, Vbn, Vcn Fig 6 The internal \structure of the block to calculate the flux linkages D. Simulation model of Vbn Vbn =Vbo Vno.. (25) Output Vbn E. Simulation model of Vcn Vcn =Vco Vno.. (26) Output Vcn VI. SIMULINK MODEL OF THREE PHASE INDUCTION MOTOR Fig.7 Internal structure of block to calculate the currents i ds, i dr, i qs, i qr and fluxes Ψmq, Ψmd Fig.4 The three-phase Induction motor MATLAB/Simulink model F. Contents of Induction motor block Fig.8 The implementation of the torque equation,te Fig 5 Internal structure of three-phase Induction motor d-q model Fig 9 The implementation of the angular speed equation,ωr 33

4 Volume-3, Issue-3, March-215 Fig.12 The implementation of current calculating block G. Results of Torque-time and Speed time characteristics T o r q u e Fig 1 The implementation of flux linkage equation By using the previously calculated flux linkages,the magnetic flux linkages can be calculated S p e e d Fig 13 Simulation output of Torque-time and Speed time characteristics Obtained Speed = 133 rad / sec = rpm H. Results of Torque-time and Speed time characteristics for T L = 2.5 T o rq u e S p e e d Fig 11 The implementation of Ψmd,Ψmq calculation block Fig14 Output torque & speed characteristics with sinusoidal input 34

5 CONCLUSION After modeling of three-phase inverter,we get phase voltage of magnitude 2V. Then feeding these voltages to three phase induction motor, we observed the torque Vs time and speed Vs time characteristics. Then observed speed is 133 radian/second which is equal to127.7.(as 1radian/second =3/п) and for load torque = 2.5, speed = 12 rpm. REFERENCES [1]. Byoung-Kuk Lee, Simplified function simulation model for 3 phase voltage source inverter using switching function Volume-3, Issue-3, March-215 concept, IEEE transaction on Industrial Electronics,Vol.48,No.2,April 21. [2]. Adel Aktaibi & Daw Ghanim M. A. Rahman Dynamic Simulation of three phase Induction Motor using MATLAB Simulink,IEEE,Faculty of Engineering and Applied Science [3]. P. N. Enjeti, P. D. Ziogas, Analysis of A Static Power Converter under Unbalance: A Novel Approach, IEEE Trans. Ind. Electron., vol. 37, no. 1, pp , Feb [4]. P.S.Bhimra, Power Electronics, Khanna publication,3 rd edition 23. [5]. Muhammad.H.Rashid, Power electronics circuits devices and applications,3 rd edition 212. [6]. Ned Mohan, Power Electronics Converters, Applications and Design, John wiley and sons Inc., New Delhi, 3rd Edition